Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!portal!cup.portal.com!lan
From: lan@cup.portal.com (Los Altos Networks)
Newsgroups: comp.dcom.modems
Subject: Re: Modems with cellular telephones
Message-ID: <35441@cup.portal.com>
Date: 31 Oct 90 19:23:45 GMT
References: <9010262354.AA04244@alw.nih.gov>
Distribution: na
Organization: The Portal System (TM)
Lines: 65


	Roger,
		I did a lot of work with the TELEBIT CellBlazer for
	TELEBIT while I was with them.  Let me give you the full
	scoop so you will know what you are getting your self into.

		So far, the responses I have seen are fairly accurate
	as to the CellBlazers performance.  Realistically, I have seen
	8,000 bits per second going cellular-to-cellular and 12,000 bps
	going cellular-to-land line.  This is using TELEBIT PEP and special
	register settings in the modem which affect the PEP packetization
	and use special algorithms to handle station-to-station hand-off
	at the cell.  There is a bit of a write-up on this available from	
	TELEBIT tech support or sales support called:  TELEBIT PEP MODEM
	CONSIDERATIONS FOR ADVERSE COMMUNICATIONS LINKS.  Please request
	this from them.  If you have any trouble, let me know and I'll
	send you a copy.

		Now here's the hard part.  The CellBlazer standalone requires
	an external 120V AC power source.  Just like a regular standalone
	TELEBIT modem.  This means you need a 12VDC-to-120VAC converter and
	a hefty car battery.  The CellBlazer PC-AT card will draw power from
	your laptop, but chances are it will draw so much power as to drain
	your laptop battery twice as fast as usual.  Power to the CellBlazer
	is non-trivial.

		Next.  The cellular phone interface.  Here's the real bitch.
	There is no standard for RJ-11 interfaces to cellular phones.  This
	means that there is a different interface adaptor for EVERY cellular
	phone made, a different price for the interface, and some phones
	with no such interface available.  These interfaces are usually
	referred to as FAX interfaces.  Tellular and their CellJack product
	are the most commonly used interface by TELEBIT in their demos.  Also,
	you should get an active (amplified/filtered) interface if possible.
	The Passive interfaces tend to lower the signal strength of the
	modem to the cellular phone.  There may be an additional power require-
	ment for the interface, as well :-(.  Ther interfaces tend to run
	from $500 and up.

		The cellular phone should be set to its maximum VOICE output
	volume level.  This will assure maximum signal strength.  The
	Modem is also adjusted for boosted signal strength via its registers.
	Experimentation is conducted to find the best settings for the
	modem and phone.  This might have to be done everytime that you
	are at a new remote site or are mobile.  Cellular carriers may also
	present a problem due to their carrier specs.  Some companded channels
	or digitally encoded channels may present a barrier to the PEP
	modulation which will either lower throughput or kill transmission
	altogether.

		With these issues in mind, I wish you good luck!  If you
	are interested in more info or acquiring a CellBlazer, give me a
	call.

===============================================================================
Cerafin E. Castillo                       ||      //\\  ||\\  ||
Network Consultant                        ||     //__\\ || \\ ||  Los Altos
Los Altos Networks                        ||    // ---\\||  \\||  Networks
340 Second St. #6                         ||___//      \||   \\|
Los Altos, CA  94022
(415) 941-8031      UUCP:     {apple,sun,uunet}!portal!cup.portal.com!cec
                 NTERNET:     cec@cup.portal.com

                      "...No hay mal que por bien no venga..."
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